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Outerbridge—The Metallurgy and Assaying, etc. 


281 


THE METALLURGY AND ASSAYING OF THE PRECIOUS 

METALS USED IN COINAGE. 1 


[Abstract of the first of a course of two lectures, delivered before the members of 

the Franklin Institute.] 

By Alexander E. Outerbridge, Jr., Assay Department, 

U. S. Mint, Philadelphia. 

ON GOLD. 

The book of nature is a vast volume, from any part of which we 
may obtain wonderful sources of instruction and entertainment. 
Whether we contemplate the immensity of the vault of heaven with 
its innumerable suns revolving in their orbits, or whether we examine 
the tiniest blade of grass or the sting of the smallest bee, we find 
equally interesting subjects for study. It is one chapter, nay, rather 
one small page, of this great book, which I propose to open for you 
this evening, and my subject possesses one material advantage in its 
novelty in a lecture course. 

The history of the precious metal which we call gold, carries us 
far back to the first records of the civilization of the human race. 
There is every probability that gold was the first metal known to 
man. Centuries before its use as a medium of exchange or unit of 
value, it was known and highly prized as an article of ornament. 
The ancient symbol of gold among the Egyptians was a circle, which 
typified to their minds the idea of perfection and divinity. 

In the Old Testament we find very frequent mention of gold, and 
the vast amounts of precious metal used by King Solomon in the 
adornment of the Royal Palace and the Holy Temple excite our 
wonder and admiration. 

The marvelous accounts related by the classic writers of the great 
quantities of gold possessed by the Oriental monarchs of antiquity 
must, of course, in some cases be accepted cum grano salts , and 
yet the recent archaeological and treasure discoveries of General 
Di-Cessnola, in Cyprus, and of Dr. Schliemann at Mycenae, are at 

1 As the lectures were not delivered from manuscript, this abstract for the Journal 
has been prepared from memory, assisted by bri6f notes of headings. It has been 
found necessary, on account of limited space, to omit some portions, and to curtail 
others. 

Whole No. Vol. CIII.— (Third Series, Yol. lxxiii.) 



20 






282 


Chemistry , Physics, Technology, etc. 

least partial confirmations of the stories related by Herodotus, 
Pliny, Homer, and other ancient authors. The beautiful collection of 
Etruscan and Phoenician golden ornaments—amulets, rings, fibulae, 
etc., exhibited in the Castellani collection at the Centennial Exhibi¬ 
tion, is a proof of the antiquity of the art of refining gold and work¬ 
ing it into artistic forms of great beauty. Indeed the method of 
joining microscopical particles of gold, forming the ornamentation 
called “ granulated work,” is a marvel to modern experts. 

I wish you to pause with me for a moment to consider a phase in 
the history of the precious metals of absorbing interest—I allude to 
the search for that ever fleeting will-o-the-wisp, the Philosopher’s 
stone. Although we may laugh at the delusions under which the 
enthusiastic alchemists of the middle ages labored in their search for 
that elixir-vitce which was to enable them to cure all ills, to prolong 
life to an indefinite period, and to transmute the - proe f ou s- metals 
into gold, we must not forget that we owe to their labors many valu¬ 
able metallurgical discoveries. The older alchemists believed that 
the great secret was possessed by the Devil and could only be pro¬ 
cured at the expense of the soul—w T hile the more modern enthusiasts 
relied upon earthly means, and they accordingly triturated and boiled 
together the most heterogeneous compounds. Thus, in an old work, 
called the “ Gold maker’s guide,” there appears this amusing recipe: 
u Take of the gall of a black tomcat, killed when the night approach- 
eth, 1 part; of the brains of a night owl taken from out its head 
when the morning dawneth, 5 parts; mix in the hoof of an ass when 
the tide turneth ; leave it until it doth breed maggots ; place it on thy 
breast-bone when the moon shineth bright—and—thou wilt see a 
sight which the eye of mortal man ne’er beheld afore.” Again, 
“Hide and couple in a transparent denne, the Eagle and the Lyon, shut 
the doore close, so that their breath go not out, and strange ayre 
enter not in ; at their meeting the eagle will tear in pieces and devoure 
the lyon and then be taken with a long sleepe.” The explanation of 
such riddles is simple enough when we have the key; for example, 
I have in my hand a glass vessel containing gold foil; this is typified 
by “the lion.” I now cast in “the eagle,” viz.: a little mercury; 
the mercury quickly forms an amalgam with the gold and becomes a 
sluggish or pasty mass, i. e. “is taken with a long sleepe.” 

Numerous guides appeared from time to time, but, unfortunately, 
those which were written plainly never yielded a stone, while those 






283 


Outerbridge—The Metallurgy and Assaying, etc. 

written enigmatically could not be understood.* This mysterious 
manner was not always owing to an intention to deceive—many phil¬ 
osophers believed it was wicked to reveal the secrets of nature to the 
vulgar people, and might even cause the death of the writer. 11 So 
strong was the faith in the power of transmuting base metals into 
gold, that Henry VI of England issued a royal proclamation, in the 
year 1423, encouraging the art of gold making, in order to obtain 
means to pay the state debt. Edward IV, in 1476, accorded to a 
company u a four yeare privilege of making gold from quicksilver. 1 * 1 

Our limited time will merely permit us to glance at these interest¬ 
ing by-paths in the history of the precious metals, and we are now 
prepared to investigate the 

PHYSICAL AND CHEMICAL PROPERTIES OF GOLD. 

You are all, doubtless, familiar with the rich orange-yellow color 
of gold, and yet but few of you have seen the royal metal in' a state 
of purity. In this little porcelain saucer I have fastened with 
mucilage a number of granulations of chemically-pure gold. This 
gold is prepared with the most scrupulous care in the Assay Labora¬ 
tory of the Mint, for test purposes, and is absolutely free from foreign 
substances. 

By the aid of the improved form of megascope, devised by the 
Secretary of the Institute, Mr. J. B. Knight, I shall project the mag¬ 
nified image of these beautiful granules upon the screen. There, you 
see, they retain their natural brilliant lustre, golden color and 


* In 1649 there appeared, “A master key to the opened heart of fatherly philos¬ 
ophy, and the “Childbed of the philosopher’s stone.” 

In 1700, “Philosophical field sports and nymph catching,” and the “Brightly 
shining sun in the alchemical firmament of the German horizon,” “ Chymical moon¬ 
shine,” etc., etc. 

u Wilhelm von Schroeder, in 1684, wrote a book called “ Necessary Instructions in 
the Art of Gold Making,” in which he says: “When philosophers speak openly, a 
deceit lies behind their words; while when they speak enigmatically, they may be 
depended upon.” 

iU The Danish ducats of 1647 were made of gold obtained, as it was believed, from 
artificial means, by the alchemist of Christian IV, named Caspar Harbacli. So under 
the Emperor Ferdinand III, in 1648, a large medal was struck from artificially-pre¬ 
pared gold. In like manner the ducats struck under Landgrave Ernest Lewis, of 
Hesse Darmstadt, were of artificial gold, prepared, it was said, by the transmutation 
of lead.— Reducer's Manual. 




284 


Chemistry , Physics , Technology , 


appearance of solidity. 1 So much for the color of gold by reflected 
light. Here is a sheet of gold-leaf, mounted on glass ; it is partially 
transparent, and you might suppose that the transmitted light would 
also have the same orange-yellow color; let us see. I place the leaf 
in the oxy-hydrogen lantern, and the disc of light upon the screen is 
tinged a decided bluish green . This property of reflecting one color 
and transmitting another, is peculiar to gold. We are thus led, by a 
natural association of ideas, to the question, how thin is this sheet of 
gold-leaf? 

The wonderful malleability and ductility of gold was a property 
well know T n to the ancients. Homer speaks of the art of gold beat¬ 
ing, and Pliny mentions that an ounce of gold was beaten into 750 
leaves, each leaf being about four fingers square. Gold leaves of 
extraordinary thinness have been found on the coffins of the Theban 
mummies. The rude specimens of gilding on the walls of the Peru¬ 
vian temples, and the palace of Tippo-Sahib at Bungalore, prove its 
extensive application in ancient times. We also have biblical 
authority to the same effect. 

Experiments made in modern times have shown that a grain of gold 
can be beaten out so as to cover a space of 75 square inches, having 
a thickness or rather thinness of ^^ 5 Q - part of an inch. While 
reflecting upon this remarkable fact, the thought suggested itself to 
me, that the film of metallic gold deposited by means of the galvanic 
battery must be far thinner. And as the art of gold plating is so 
extensively applied to a great variety of ornamental metal objects, it 
seemed an interesting query, how thick a film is required to produce 
a fine gold color ? On inquiring into the subject I did not find that 
any careful notes had been recorded, and I was led to try some exper¬ 
iments with rather interesting results, although they are not yet 
finished. Here are two highly burnished plates of metal, looking like 
pure gold; they have a metallic surface of twenty square inches each; 
these plates were cut from a strip of copper which I had rolled down 
to a uniform thickness of yoVo °f an inc ^- They were boiled in 
alkali to remove grease, and accurately weighed on an assay balance 
of extreme sensitiveness. 

A “ gold blush ” of sufficient depth to produce this fine gold color 
was then deposited by the battery; the strips were carefully washed 

* Several gold coins, medals and ornaments were exhibited, and elicited th e 
applause of the audience, both on account of their inherent beauty and the brilliancy 
of their reflection. 






285 


Outerbridge—The Metallurgy and Assaying, etc . 



and dried without rubbing; they were then reweighed, and I found they 
bad gained exactly one-tenth of a grain each. It is thus apparent 
that one grain of gold would cover a space of 200 square inches, 
when deposited by the battery, as compared with 75 square inches by 
beating. 

The film of gold appears evenly 
deposited, under the microscope, 
and it is more than 2 J times thin¬ 
ner in the former case than in the 
latter, or 98 0400 an inch as 
compared with - 3 6 ^ 5 Q of an inch . 1 

It is stated, that when a cylin¬ 
drical bar of silver is coated with 
gold and drawn into the fine wire 
used in embroidering housings, 
etc., one grain of gold will cover 
a length of SIS’O feet of wire. 

Gold deserves its name of a no¬ 
ble metal ” from its power of re¬ 
sisting the rusting and tarnishing 
action of the atmosphere, even 
when subjected to the severest 
trials. Kunckel kept a mass of 
gold in a molten state exposed to 
the atmosphere, for a period of 
nearly 30 weeks; at the end of 
that time it had not lost a single 
grain in weight. 

Gold may be melted at a tem¬ 
perature of a little over 2000° F. 
in a wind furnace. 

We may even cause gold to boil 

. . . r . Electric Lamp. 

and vaporize by means of the 

intense heat of the electric arc. Here is an apparatus designed to 
produce an exceedingly powerful electric current. The copper wires 


1 “A leaf of beaten gold occupies an average thickness of no more than one-fifth to 
one-eighth part of a single wave of light. By reducing the thickness of the leaf by 
solution in cyanide of potassium, I think 50 or even 100 might be included in a single 
progressive undulation of light.”—Faraday’s Researches on the “Experimental Rela¬ 
tions of Gold (and other metals) to Light.”— Philos. Trans. 
































































286 



Carbon 

Points. 


Chemistry , Physics , Technology , ete. 

t 

conveying the current terminate in two sticks of carbon placed ver¬ 
tically one above the other in the focus of the condensing lens of 
this large lantern; when the points of carbon are brought in contact 
they become intensely hot, and on separating the poles, 
the current is carried across the hiatus, by the conduc¬ 
tivity of the carbon particles. The lens projects the 
greatly magnified image of these incandescent poles upon 
the screen. 1 II In the lower carbon is bored a small cavity 
into which I place a particle of gold, and you see its 
image just appearing upon the screen as a globule becom¬ 
ing white hot; ah ! now it boils, and there darts forth an 
exquisitely beautiful tongue-like flame of vapor of gold , 
licking the carbon points, and there, upon the opposite 
electrode, are rapidly appearing small brightly shining 
beads of condensed vapor of gold, resembling spark¬ 
ling dewdrops. u 

Gold resists the solvent action of nearly all single acids, but a 
mixture of nitric and muriatic completely dissolves it as a per- 
chloride; hence the alchemists gave the name of aqua-regia to this 
combination. Here are three glass vessels containing sulphuric, 
nitric and muriatic acids, with a piece of pure gold in each one, where 
it has remained for several hours, quite unchanged. I now pour the 
contents of the last mentioned vessels together, and our gold dis¬ 
solves almost immediately. 

Having in this manner obtained a solution of gold, we are pre¬ 
pared to test it with several characteristic re-agents. I place a 
few drops of the gold solution in this little tank containing dis¬ 
tilled water, which you see reflected upon the screen; I now add a 
single drop of the solution of proto-sulphate of iron, and instantly 
a dark precipitate of metallic gold in fine division, rolls like angry 
thunder clouds over the canvas. This method of precipitation is 
used in the mint in the preparation of chemicallv-pure gold. I now 
add, to a fresh solution of gold, a drop of ammonia: a precipitate of 


I The cut shows the carbon points inverted, as they appeared on the screen. 

II The apparatus used for the development of the electric current was “ Wallace’s 
Duplex magneto-electric machine,” and was kindly furnished for these lectures by 
the manufacturers, Messrs. Wallace & Sons of Ansonia, Conn. The shaft was revolved 
at about 1200 revolutions per minute by a steam engine placed at the back of the 
stage. The light produced was remarkably steady and intensely brilliant. 

















287 


Outerbridge—The Metallurgy and Assaying , etc. 

a very different character appears upon the screen. This is the 
substance known as fulminating gold , and is a dangerously explosive 
compound ; fatal accidents have occured from its careless or ignorant 
preparation. Again, I take a fresh solution which is somewhat acid; 
into the tank, I place a thin strip of tin, it is attacked by the acid; 
proto-chloride of tin is formed, which instantly unites with the gold, 
developing very pretty purple streamlets. This is the well known 
“ purple of Cassius,” about whose chemical composition there has 
been a great deal of discussion. The Cassius purple is largely used 
in the arts, in staining ruby glass, and giving to enamel the delicate 
rose-pink color. 

SOURCES OF GOLD. 

To say that gold is at once a rare metal, and yet that it is one of 
the most widely disseminated of the metallic elements, seems at first 
sight contradictory; and yet it is, in a sense, literally true. Gold is 
found in Europe, Asia, Africa and America ; it was known, in the 
time of Herodotus, to exist in Russia in the Ural Mountains. The 
mines were afterwards re-discovered in 1743, during explorations 
ordered by Peter the Great. The gold and silver mines of Spain 
have been worked from the most remote periods; both Strabo and 
Pliny mention the abundance of the precious metals, and it is stated 
that Hannibal would have been unable to continue the war in Italy 
but for the discovery of many mines in Carthagena. China and 
Japan, India, Ceylon, Sumatra, Borneo, the Celebes and Philippine 
Islands, all add a sheaf to the golden harvest. The mountains and 
streams of Africa all contain gold. The Transvaal Republic, in 
Southern Africa, promises vast wealth of native gold to the hardy 
explorer; some magnificent nuggets were brought to us recently by 
a prospector from this almost inaccessible region. Some of these 
nuggets were for a short time placed at the Centennial Exhibition. 1 

It remains for our own country to have the honor of possessing 
the most extensive gold and silver producing regions of the world at 
the present day. California and Oregon, Idaho and Washington 
territories, Nevada and Colorado, Montana, Arizona and New Mex- 


i A facsimile of one of the largest nuggets ever found in Australia was exhibited to 
the audience. It was prepared at the Department of mines in Melbourne, and formed 
an attractive object in the Victorian Court of the late exhibition. 




288 


Chemistry . Physics , Technology , ete. 

ico, all contribute their quota. 1 Even the Philadelphia bricks, of 
which our houses are built, contain gold securely locked within their 
walls, as was proved by the interesting investigations made in the mint 
some years since. 11 Here is a speck of gold, barely visible to the 
naked eye, which was extracted at the assay laboratory from galena of 
Bucks Co., Pa., representing one part of gold in 6,220,000 parts of ore. 

GEOLOGICAL POSITION. 

Gold is found in nature in the form of dust, grains, nuggets, and 
associated with quartz, etc. “It was formerly supposed that pro¬ 
ductive gold veins were confined to the Silurian rocks, but the dis¬ 
covery of fossils of the Carboniferous period in California by 
Dr. Trask in 1854, the exploration of Professor Blake, and the sub¬ 
sequent discovery of secondary fossils in the main belt of gold bearing 
States, together with the discoveries in Hungary in 1861-62, proving 
that the rocks holding the gold belong to the latest geological periods, 
even as late as the Tertiary—all show the fallacy of the opinion that 
productive gold veins are associated chiefly with the older rocks.” 111 

MINTING. 

Gold is received at the mint in the form of native grains, dust, 
amalgam, photographers’ waste, old jewelry, dentists’ plate, etc., and 
often contains a great variety of base metals, destroying its ductility, 
and rendering it totally unfit for coin. It is necessary to eliminate 
these, and then to effect the removal of silver. We will follow in 
imagination the course of a deposit, consisting, let us suppose, of old 
coin and jewelry, as it is received at the mint counter. 

The metal is placed in a locked box, and carried to the “ deposit 


1 According to the record of Wells, Fargo & Co., the sole carriers of the gold and 
silver product of the Pacific States, the total gold product of the mines west of the 
Missouri River, for the year 1876, was $44,828,501. This exceeds the amount pro¬ 
duced in any year since 1870. The highest yearly product was $65,000,000 in 1853. 
The total gold produced since 1849 is $1,858,400,745. The total stock of gold in the 
world, at the present time, has been estimated at $5,540,000,000, with an annual loss 
by wear and tear of $15,000,000. This is interesting, but can hardly be considered 
more reliable than a guess. 

il The report of these experiments, made by Profs. Eckfeldt and DuBois, states that 
the clay contains about forty cents’ worth to the ton ; that it is homogeneously dif¬ 
fused ; and, from an estimate made of the extent of the clay bed, it was found that 
more gold lies under the paved portion of the city “ than has yet been brought, ac¬ 
cording to the statistics, from California and Australia.” 

111 Blake’s Report on the Precious Metals at the Paris Exposition. 



289 


Outerbridge—The Metallurgy and Assaying, etc. 

melting roomhere it is melted under a protective covering of 
borax, and constantly stirred, to render the mass homogeneous. It 
is then cast into a bar or “shoe” mould, and weighed; this is the 
weight at which the mint receives the deposit. A small chip is now 
cut off, for purposes of assay. A rigid analysis is made of this 
sample, and the result determines the value of the entire mass, by 
calculation to the fraction of a cent, and the depositor is paid ac¬ 
cordingly. As the largest weight used by the assayer is the demi- 
gramme (about 7 T 7 y grains Troy), and the deposit frequently represents 
thousands of dollars, it is evident that a very slight error in the 
assay would amount to a considerable sum total;* the assayer accord¬ 
ingly carries his actual analysis to the ten-thousandth degree, viz. : 
the twentieth part of a milligramme, or the yAr P art a Troy 

grain. The fine assay balances will 
indicate even a smaller weight than 
this. The assayer rolls the sample into 
a thin ribbon, for convenience of cut¬ 
ting; the weight of half a gramme of 
this gold alloy is enclosed in an enve¬ 
lope of pure lead, and melted in the 
muffle of the assay furnace, in a small 
cupel made of pressed calcined bones. 
The lead rapidly oxidizes, and in this 
condition is much more fluid than the simply 
melted precious metal; it therefore sinks 
into the pores of the cupel, carrying with it 
all the base metals originally combined in 
the alloy; the button of precious metal 
remaining is weighed, and the proportion of base metal determined; 
another weighing of the sample is made as before, to which is added 
fine silver granulations in the proportion of about two parts of silver 
to one of gold. The alloy is cupelled as before, and the silvery 
button remaining is laminated, coiled into a “cornet,” and boiled 
in nitric acid. The acid dissolves all the silver, leaving a roll of pure 


i The average weight of one “melt” of gold ingots for coin, the fineness of which 
is determined by assaying a slip cut from the first and last ingot cast, is 4000 ounces 
Troy. The value is about $75,000 in gold. Melts containing as much as 5500 ounces 
have been made, but it is found very difficult to render the metal homogeneous, owing 
to the difficulty of pushing the stirrer down to the bottom of the pot. 






























































290 


Chemistry , Physics, Technology , etc. 

gold remaining; the gold cornet is then annealed and weighed; this 
weight is the proportion of gold ; the difference between this and 
the first weight, is the proportion of silver. 1 The object of adding 

pure silver to the alloy is, in order that it 
may be present in excess ; otherwise the 
atoms of gold cover up and protect the silver 
originally present in the alloy. 

Numerous checks are employed to correct 
variations, and so accurate are these devices 
that two samples taken from the bar will fre¬ 
quently be found, after passing through the 
various chemical and mechanical operations 
of hammering and rolling, melting, fluxing 
and dissolving (providing the original melt¬ 
ing rendered the mass homogeneous), to show 
a deviation in the assay of not more than 
one-thousandth part of a single grain. The 
methods of refining gold adopted in the mints 
are so closely associated with silver, that the two will be incorpor¬ 
ated in the abstract of the second lecture. 11 



1 Strictly speaking, the gold cornet is not. absolutely pure, but contains a small 
“ sur-charge ” of silver. The weight of the sur-charge varies according to the tem¬ 
perature of the furnace and other causes. This slight but important variation is 
determined by means of “ proof assays ” of chemically-pure gold, which are invari¬ 
ably made side by side with the others, and the proper correction is made for each. 
The boiling in nitric acid was formerly effected in separate glass flasks, but a great 
improvement has been made, in comparatively recent years, whereby the cornets are 
all subjected to the same acid and the same heat. A small platinum basket, per¬ 
forated with holes, is made to contain a set of sixteen platinum thimbles. One 
cornet is placed in each, and the basket is immersed in nitric acid contained in a 
small platinum still. The boiling is effected by a Bunsen burner. When the silver 
is dissolved, the cornets are washed, dried and annealed in the basket. It is neces¬ 
sary to know, approximately, the amount of silver originally in the alloy ; otherwise, 
if too great an excess is added, one of the cornets may break up, and, becoming dif¬ 
fused through the acid, small particles will attach themselves to the other assays and 
ruin the whole set. This is a misfortune that rarely happens to a careful assayer. 

H Through the courtesy of the chief assayer, the lecturer was enabled to illustrate 
his descriptions by the aid of apparatus in daily use in the mint. Facsimiles of gold 
bars, ingots for coin, native grains and nuggets, were shown, prepared in plaster of 
Paris, and covered with gold-leaf. Large oil paintings, showing the geological struc¬ 
ture of the gold regions of California, and the methods of washing, were kindly lent 
by Professor Booth. 




























Outerbridge — The Metallurgy and Assaying , etc . 


339 


THE METALLURGY AND ASSAYING OF THE PRECIOUS 

METALS USED IN COINAGE. 


[Abstract of the Second Lecture delivered before the Members of the Franklin 

Institute.] 


By Alexander E. Outerbridge, Jr., Assay Department, 

U. S. Mint, Philadelphia. 


ON SILVER. 

In my last lecture I traced the history of gold from its earliest 
mention in the Bible, in the marvelous accounts of the early classic 
authors, and of the alchemical writers of the middle ages, down to* 
the production of the present day. 

Silver was likewise known from the most ancient historic period,, 
and even antedates gold as a medium of exchange. Its frequent 
mention in Scripture proves its familiar employment among the Jews. 
The shekel was a silver coin, and as it is very interesting, not only 
historically, but as revealing the state of coinage in the time of 
Simon Maccabseus, whose reign began 143 B. C., we will project its 
image upon the screen by means of the megascope. 

On the reverse side you see the 
budding rod of Aaron, with the 
Jerushalaim ha-kedoshah 
in the Samaritan character, which 
is, translated, Jerusalem the holy. 

On the obverse is the pot of 
manna, with the words iShekel of of simon macoab^us. 

Israel. This is one of the rarest and most remarkable coins in the ; 
mint cabinet. 1 

i Several curious old silver coins were used in illustration ; among the most interest¬ 
ing were the stater, or 4 drachms of Athens, 2100 years old, showing the sacred owl. 
The stater of Alexander the Great, B. C. 386—323, showing the head of A. as 
Hercules with the lion’s skin. A silver coin of Sapor, one of the Magian or fire wor¬ 
shiping kings of Persia, preceding the rise of Mohammed, A. D. 300. Denarius of 
Tiberius, A. D. 14-37, this was the penny of the New Testament. A silver coin struck 
in the time of the Roman Emperor Vespasian, A. D. 69-79, to commemorate the 
destruction of Jerusalem, with a figure of a weeping woman. And, finally, proof 
coins of our own mint, for 1877. The slow growth of art and gradual development of 
mechanical improvements in coinage, were very rapidly demonstrated in this manner. 

Whole No. Yol. CIII.—(Third Series, Vol. lxxiii.) 




24 




























340 


Chemistry, Physics , Technology , etc . 


PHYSICAL AND CHEMICAL PROPERTIES. 

We are at once impressed with the brilliant lustre and pure white 
color of the virgin metal. This property is beautifully shown by the 
little granule of chemically-pure silver reflected on the screen, and 
magnified to the size of half a ton. 

In its malleability and ductility, silver ranks second only to gold. 
Here is a book of silver leaves. They are so light that they float 
about on the surface of water, and if I hold some of them over the 
ascending current of warm air from the register on the floor, they 
are wafted through the room like thistles in the breeze. 

Silver dissolves readily in nitric and in concentrated boiling sul¬ 
phuric acids. Both of these solvents are used in the mints for the 
refining of the metal. A great number of re-agents precipitate 
silver from its solution. We will merely consider a few of the most 
characteristic and important. This tall jar contains salt water, and 
here is a silver quarter dissolved in acid ; they both form clear solu¬ 
tions. By pouring the silver into the salt we obtain a white, floccu- 
lent cloud, falling like a miniature snow shower. The fickle chlorine 
gas, which was before united with the sodium, forming common salt, 
has changed partners with the nitric acid, and we have as a result, 
chloride of silver precipitated and nitrate of soda in solution. This 
test is of great value in the analysis of silver, and is an exceedingly 
delicate one, as I shall now endeavor to show you. . I am holding in 
the forceps a tiny particle of silver which weighs just one-hundredth 
part of a single grain. I put it into a test tube containing a few 
drops of nitric acid, and it is immediately dissolved. The little glass 
tank in the lantern, reflected on the screen, contains a common sea¬ 
water bath, sufficiently enlarged to make a pretty formidable wave. 
I now add our drop of nitrate of silver, and I think you can all 
notice a cloud, the size of a man’s hand, forming upon the screen. 

Silver melts and volatilizes at a much lower temperature than gold ; 
I place a particle of it on the lower carbon electrode, and you all 
see the superb emerald-green flame it produces, which is even more 
beautiful and brilliant than was the vapor of gold. 

SOURCES IN NATURE. 

Silver is found in the metallic state nearly pure, sometimes in 
enormous masses, weighing several hundredweight; but it is more 
frequently combined with other elements, such as sulphur, antimony, 


341 


Outerbridge—The Metallurgy and Assaying , etc . 

lead, arsenic, etc. The process of extraction from the ore is, there¬ 
fore, much more complicated than is the case with gold. It is also 
found over a wider range of geological periods. It occurs in true 
veins in the older crystalline and metamorphic rocks, in calcareous 
rocks, and even in the carboniferous period. The large colored 
geological chart of the world, together with the paintings, will serve 
to give you a pictorial impression of the natural distribution of the 
precious metals, and the means adopted for their separation. 

My friend, Mr. J. A. Clay, whose valuable cabinet of minerals 
some of you may have seen, has kindly placed at my disposal his 
gold and silver specimens; many of these are quite rare, and the 
megascope will enable you all to appreciate their beauty. Perhaps 
one of the most remarkable of these is the ruby silver, enclosed in a 
transparent crystal of quartz. 

The most famous mines of the old world are to be found at Kongs- 
berg, in Norway, and at Sala, in Sweden. The silver mines of Spain 
have been worked from the most remote period by the Phoenicians, 
Romans and Moors in turn. In fact nearly all the countries of 
Europe have added their quota to swell the general stock in existence, 
both of silver and gold. 

Mexico formerly produced two-thirds of the product of the whole 
w T orld. You all remember the famous cake of silver that attracted so 
much attention in ,the Mexican Court at the Centennial Exhibition. 
This cake was afterwards cut up by steam shears, and brought to the 
mint. It weighed about 4000 pounds, contained of pure silver, 
and was worth $68,149. 

The famous mines of Potosi, in Bolivia, were discovered in 1545, 
and were estimated by Humboldt to have produced $1,150,000,000 
worth of silver. 

Coming now to the United States we find here the greatest mines 
of the world. Nevada and Colorado are treasure houses of appa¬ 
rently inexhaustible wealth. The presence of veins of silver through¬ 
out the territory of Nevada was comparatively unknown until 1859, 
when the Comstock vein was discovered. a The region was then 
regarded as an irredeemable wilderness, a land of deserts and death, 
over which the early pioneers had passed as rapidly as possible in the 
tide of emigration to the gold regions of California. The scene has 
changed, Nevada from a comparatively unknown portion of Utah 
became first a territory and then a state in the Union. The valleys 
and deserts resound with the shrill whistle of engines and falling of 



342 


Chemistry , Physics , Technology , ete. 

stamps. The little valleys are brought into cultivation; graded roads 
are made over apparently impassable mountains; mails arrive and 
depart daily, and the telegraph connects the business centres with 
those on the Pacific and Atlantic coasts. All this has resulted 
chiefly from the discovery of the celebrated Comstock lode, which 
has already added nearly $80,000,000 in value to the bullion of the 
world.” 1 

In 1876, the Consolidated Virginia mine alone is reported to have 
yielded 145,666 tons of ore, the value of which was $16,661,940. 
Colorado yields at the present time a daily average of $15,000 in 
silver, and $10,000 in gold. The mines of Utah yield a daily 
average of $12,000 in silver. 

REDUCTION OP ORES. 

The ancient method of extracting silver from its ores was exceed¬ 
ingly crude, requiring a period of several months in the operation. 
In the old Mexican process, the ore was ground to a fine powder in 
circular paved pits or mills called arrastras, by means of large stones 
attached to a shaft drawn round by mules (resembling the manner in 
which clay is still mixed in some of our brickyards); water was 
added and the argentiferous mud was piled into heaps and left exposed 
for a considerable time to the action of the atmosphere. It was then 
mixed with common salt and copper pyrites called magistral by driving 
mules backward and forward over the mass. Mercury was added 
which combined with the silver to form amalgam and the dross washed 
away. 

The excess of mercury was removed by squeezing the amalgam in 
canvas or chamois skin bags. This method is said to have been 

1 “ From the Comstock the explorations extended in all directions, and resulted in 
the discovery of gold and silver hearing veins in most of the principal mountain 
ranges that traverse the great basin in a general north and south direction. First the 
metal was traced southward to Esmeralda, Mono, Coso, Walker’s River, Owen’s River, 
and the slate range near the southern end of the Sierra Nevada. Eastward the Hum¬ 
boldt mines, Reese River, Goose Creek, Egan Canon, and Utah Mines, were reached 
in succession, and the discoveries have been extended eastward to the ranges of the 
Rocky Mountains, where the prospectors met those of Colorado. Northward in con¬ 
nection with the gold prospectors of Oregon, the precious metals were traced into 
Idaho, Montana, and British Columbia, and southward, veins have been discovered 
along the ranges reaching into Arizona, extending the silver region to Sonora, thus 
connecting the whole with the great metalliferous belt of the Mexican plateau; and with 
the discoveries of the extreme north, proving a continuous zone of mineral wealth 
through North America, from Panama to the Arctic Sea.”— Prof. Blake's Report upon 
the Precious Metals. 




343 


Outerbridge—The Metallurgy and Assaying, etc, 

invented in the year 1557 by a miner named Bartholomew de Medina. 
Nearly all the modern improvements, are merely mechanical modifi¬ 
cations of detail, but the advantages of machinery are so great that 
as much can now be accomplished in a few hours as formerly required 
several months. 

The usual method at present adopted is to roast the silver ores 
containing sulphur with from six to twelve per cent, of common salt. 
About 1000 lbs. of ore constitute a charge. The heat volatilizes the 
sulphur and the chlorine unites with the silver. After the ore has 
swelled into a spongy condition it is thoroughly sifted and placed in 
barrels holding 1000 lbs. each, mercury is added and the barrels are 
revolved for about 20 hours. Modifications of this process are 
adopted in some cases, to shorten the time ; the mercury is sometimes 
delivered in a fine spray while the ore is kept hot. In order to sep¬ 
arate the mercury the amalgam is dried, rolled into balls, and placed 
in hermetically-sealed retorts. The mercury is driven over and con¬ 
densed, and the silver is cast into bars (called gigs) for shipment. 
Efforts have been made to effect the removal of the silver without 
the aid of mercury, and several methods of solution and precipitation 
have been devised. Ziervogel’s process is exceedingly ingenious. 
The matt , consisting of sulphurets of silver, copper and iron, is 
roasted. The copper and iron first change to sulphates and then to 
oxyds. The sulphuret of silver also subsequently becomes sulphate, 
and if the heat were continued would be reduced to the metallic state ; 
as this is not desired, the roasting is discontinued, and the silver is 
found as a soluble sulphate , which is then dissolved in hot water. The 
silver is precipitated by means of copper plates. The principal objection 
to this method of reduction is that the presence of certain impurities, 
such as antimony or arsenic, cause the formation of insoluble salts, 
which retain a portion of the silver. 

Yon Patera’s process consists in converting the silver into a 
chloride by roasting with salt. It is then dissolved in a cold dilute 
solution of hyposulphite of soda. It is next precipitated in the form 
of sulphide by the addition of polysulphide of sodium, and finally 
reduced to the metallic state by melting in a furnace while exposed 
to the atmosphere. 

All the processes of solution are comparatively modern, and pos¬ 
sess advantages in several ways over the old amalgamation methods. 


844 


Chemistry , Physics , Technology , etc. 


MINTING. 

Silver bullion is received at the mint in the form of bars, pigs,. 
dor6 silver, old plate and coin. We have even received, in former 
days, whole altars of silver from Mexico, and Saints innumerable, 
which were ruthlessly cast into the fiery furnace. 

The bullion is frequently rendered exceedingly “short” or brittle 
by the admixture of base metals. These, of course, require to be 
eliminated in order to render the metal fit for coinage, and the pro¬ 
cess is technically called “ toughening.” The metal is melted in a 
sand pot with an oxidizing agent, such as nitre, together with a pro¬ 
tective covering of borax. The oxygen of the nitrate of potash 
combines with the base metals, forming volatile oxides; these are par¬ 
tially dissipated and partially dissolved in the borax. The precious 
metal is then cast into bars, and still another process, known as 
“parting,” is required to separate the silver from the gold. For 
this purpose the silver deposits containing gold, and the gold deposits 
containing silver, are melted together so as to make the relative pro¬ 
portions about two pounds of silver to one of gold; formerly three 
parts of silver were considered necessary ; hence the old name, “in- 
quartation.” The metal is broken up into granulations by pouring 
it from the melting pot into ice-water; these are placed in large 
porcelain jars having a capacity of 50 gallons each. Nitric acid is 
added and steam heat applied for several hours. The silver is con¬ 
verted into a soluble nitrate, and the gold settles to the bottom in the 
form of brown powder. 

By means of a large gold siphon the solution of silver is transferred' 
to a wooden vat containing salt water, having a capacity of 1200 
gallons. The precipitated chloride of silver is collected on filters, 
washed, and reduced to the metallic state by means of granulated 
zinc and dilute sulphuric acid. Here is another instance of the base 
inconstancy of the pungent chlorine; having first deserted the sodium 
for the silver, it already sighs for new elements to conquer, and takes 
to itself the metal zinc, leaving the silver without a partner. The 
silver does not now present the beautiful appearance of the virgin 
metal, but requires purification by the “ tryall by fire.” It is 
accordingly pressed into large cakes, dried in an oven at a moderate 
heat, and melted in large crucibles. It is then cast into fine bars for 
stamping, or the requisite proportion of of copper is added for 
coin ingots. 


345 


Outerbridge—The Metallurgy and Assaying , etc. 

In most of the foreign mints, as well as at the assay office in New 
York, the parting is effected by means of concentrated boiling sul¬ 
phuric acid in cast iron kettles. The silver and copper are converted 
into soluble sulphates, while the gold remains untouched. Sulphur¬ 
ous acid gas is largely developed ; this is sometimes conducted into 
leaden chambers and condensed into sulphuric acid. The silver is 
then reduced to the metallic state by means of copper plates. The 
sulphate of copper formed is crystallized in flat pans or vats, and 
becomes a valuable product. The advantages of this method are in 
the cheapness of sulphuric acid as compared with nitric, and in the 
fact that all the copper originally in the alloy is recovered in the form 
of blue stone, while in the nitric acid process it is lost in the solution 
of nitrate of soda. 

The most recent improvement in refining which seems to combine 
the three valuable concomitants, of cheapness, simplicity and dis¬ 
patch, is the chlorine process devised by Professor F. Bowyer Miller, 
of the Sydney Mint, Australia. A current of chlorine gas is passed 
through the metal while in a molten state; the gas combines with 
avidity with all the metals except gold, converting the base metals— 
such as lead, zinc, tin, antimony, etc.—into volatile chlorides, which 
escape up the chimney. The chlorides of silver and copper being 
comparatively non-volatile, are retained by a protective covering of 
melted borax, and, being lighter than the molten gold, they float upon 
its surface. The pot is then removed from the fire, the gold quickly 
“ sets,” and the combined chloride of silver and copper is poured 
into moulds. 

Extended tests of his process were made by Professor Miller at 
our mint, a few years since, which proved entirely successful. The 
gold was found to be as nearly pure as by the other methods in use, 
and the chloride of silver may be reduced in the ordinary way. This 
ingenious method was devised for the especial purpose of recovering 
the silver in the native gold of Australia, which often amounts to as 
much as 14 per cent., but which was formerly lost to the colony, 
owing to the too great expense of acids in that country. 

ASSAYING. 

In my first lecture I gave you a brief outline of the method of 
assaying gold by cupellation. Silver was also formerly assayed in 
the same way, but it was long known that the result was not quite 


346 


Chemistry , Physics , Technology , etc. 


accurate, owing to the partial volatility of the metal. Experiments 
were instituted by the French government, which resulted in the 
beautiful u volumetric process ” devised by Gay Lussac. This is 
one of the most accurate methods known to chemical science, and so 
-complete was Gay Lussac’s original description, that but little room 
has been left for any improvements, and many thousands of dollars’ 
worth of silver are rapidly and accurately assayed every day in the 
mint in this way. The rationale of Gay Lussac’s method is quite 
easy to understand, viz., a given proportion of chlorine will precipitate 
a definite amount of pure silver. 

We prepare two solutions of common salt water (chloride of sodium), 
one is known as the “ normal solution,” the other as the “ decimal 
solution,” one begins and the other finishes the assay. Here is a 
pipette holding just one hundred grammes of the normal solution, 
which is made of such a strength that it will precipitate exactly one 
gramme of pure silver. In this bottle, I have a piece of a silver coin of 
a definite weight, dissolved in nitric acid, and when the pipette charge 
of normal salt water is added to it, you see the dense white precipitate 
which permeates the whole liquid. I now agitate the bottle rapidly 
for a few moments and the precipitate falls to the bottom, leaving a 
clear solution above. Is any silver still unprecipitated? Let us see. 
Here is a glass tube with graduated divisions, each division marks 
one-hundredth the capacity of the large pipette, and here is a solu¬ 
tion of salt just one-tenth the strength of the other. I allow the 
charge of decimal salt water contained in one division of the glass 
tube to flow over the surface of the silver solution in the bottle, and 
a cloud is forming on the top. Now, as this charge of salt is y 1 -^ the 
strength and -y^ the volume of the normal solution before added, I 
know that I have precipitated just t -qVo as muc h silver , or one milli¬ 
gramme. The bottle is again agitated until, after four decimal charges 
have been added, only a very faint shadow of a cloud appears, and I 
am now sure that all the silver is precipitated. A simple rule-of- 
three sum, gives us the proportion of fine silver in the original weight 
of alloy. 1 It is not necessary to weigh the precipitate, and even the 

1 The gramme with its decimals is universally adopted by assayers for accurate 
scientific work, the jewelers’ “ carat” having been entirely discarded within the last 
half century. Twenty-four carats represent purity, or 1000 fine. 18 carats mean 
two-thirds fine or 760-thousandths. Our “ standard ” for both gold and silver coin is 
900 parts o'f precious metal, and 100 parts of copper; in other words it is nine- 
tenths fine. 






34T 


Outerbridge—The Metallurgy and Assaying, etc. 

calculation is saved by using Gay Lussac’s tables. But perhaps you 
may think that the strength of the salt solution must vary with 
changes in the temperature; so it does, but this and other minor 
sources of error are corrected by testing the strength of the solution 
every day by means of a “proof assay,” made of chemically-pure 
silver. 1 

SPECTRUM ANALYSIS. 

Most of you are, no doubt, familiar with the principles of the capti¬ 
vating study of spectrum analysis. You know that a beam of white 
light from the sun, or from this powerful 
electric lamp, is a very complex thing indeed. 

It is composed of a number of different and 
distinct rates of vibration of the luminiferous 
ether, which may reveal themselves to our 
physical sense of sight as a band of beautiful 
colors (as in the rainbow), but which are 
ordinarily so blended together upon the ret¬ 
ina that we fail to distinguish the component 
elements; just as when we listen to a sym¬ 
phony played by a fine orchestra, we appre¬ 
ciate the combined harmonies while we lose 
the sound of the individual instruments. 

By inserting this prism in the path of the 
beam of white light coming from the electric 
lamp, we can sift out the primary rays, and 
now we have upon the screen a palette of the 
purest rainbow colors, spread by nature’s 
ow r n artistic hand, and shading into each stand, with two prisms. 
other with an exquisite blending far surpassing the fondest dreams 
of a Titian or a Turner. 

What would be the effect if, in place of this brilliant chromatic 
symphony , we could produce a luminous solo by means of a light of a 
single color ? 

There is a fundamental mono-chromatic note in the spectrum, which 
I wish to have as familiar, to your eye, as our national tune is to 

1 Mercury is the only foreign element liable to cause an error in the humid assay. 
Its presence, even in minute quantity, may be detected by a peculiar haziness in the 
liquid. A mere trace will prevent the blackening of the chloride of silver in strong 
sunlight. I believe that this is a fact not generally known. 


































348 


Chemistry, Physios, Technology , etc. 

your ear, for it is the key-note to the whole study of spectroscopic 
analysis. I therefore place in the electric arc a particle of sodium; 
this metal is capable of vibrating, when vaporized, at only one note 
of color , and hence you now see upon the screen a single band of 
intensely yellow light. Please to fix the position of this yellow line 
in your memory. It is called the “ D” line, and is regarded by spectro- 
scopists as a sort of tuning fork by which the positions of all the other 
notes in the chromatic scale are compared. I shall now vaporize a 
particle of pure gold and pass its light through the prism, ah ! there 
it has written its signature upon the screen, in lines of brilliantly 
colored light, which nature never counterfeits. 

Next we will call for the autograph of silver, and you see the 
beautiful green lines so characteristic of this metal. Then comes 



APPARATUS FOR PROJECTION OF SPECTRA. 


copper, determined to outshine the others in its bold chirography; 
and, finally, when we vaporize an alloy of all three metals, we have 
the signatures of each written without confusion, and endorsed by 
the infallible authority of nature herself. 1 

We have thus seen that the terrestrial elements (even when alloyed 
together), in the state of incandescent vapor, write their own dis¬ 
tinctive autographs in the spectroscope, whereby each one may be 
easily recognized. But, you may ask, can these signatures also tell 
us the relative proportions in which the metals are combined? “Ay, 
there’s the rub.” This is the great problem that scientists are try¬ 
ing to solve to-day, and which I hope, and almost believe, we will 

* By plugging the metal firmly into the cavity in the lower carbon, and filing it 
down to a cone, thus forcing the current to pass constantly from the molten 
globule, an uninterrupted spectrum was obtained in each experiment. 








































349 


Outerbridge—The Metallurgy and Assaying, etc . 

yet see accomplished. A step in this direction, which seemed to 
promise hope ot success, was made some time ago by Mr. J. Norman 
Lockyer, the English astronomer. You know that when powerful 
electric sparks (from an induction coil) are passed between two 
terminal points of metal to be examined, a small portion of the 
metal is vaporized; its spectrum is then examined through an 
instrument of this kind. 



Mr. Lockyer noticed while studying these luminous autographs, 
that when he separated the metallic electrodes, causing the spark to 
leap a greater distance through the air, the spectral lines no longer 
continued to cross the entire field of vision, but certain of them broke 
in the middle ; and upon further increasing the distance between the 
electrodes, the hiatuses in the spectral lines increased proportionately,, 
but unequally with different alloys. Upon this discovery Mr. Lockyer 
based the theory of a possible quantitative analysis. 

The spectroscope was known to be marvelously sensitive to the 
impression of these autographs, and it therefore appeared plain that 
could such a method of analysis be reduced to a practical basis, its 
value would be immense in assaying metals used in coinage. For 
although the present modes of assaying precious metals have been 
brought to great perfection, yet the process is slow and tedious, 
requiring many chemical operations and great delicacy of manipula¬ 
tion ; and “ there is something captivating in the idea of a determi¬ 
nation, as it were, by a flash of lightning, or in the twinkling of an 
eye, what proportion of gold or silver is present in any bar or coin.” 


















350 . Chemistry, Physics, Technology, etc . 

It was with the hope of reducing this beautiful theory to practice 
that I undertook, with the approbation of the chief assayer of the 
mint, an extended investigation in the assay laboratory, a portion of 
the work being performed at the University of Pennsylvania with the 
excellent apparatus and appliances afforded in the new college building. 
As the result of this investigation was published in the form of a report 
to the assayer, in the Proceedings of the American Philosophical 
Society, and afterwards as an article for the Journal of the 
Franklin Institute, it is unnecessary to do more than allude to a 
few of the experiments. 

Various grades of alloys of gold, silver, and copper, were pre¬ 
pared, and their exact composition determined by careful assays. A 
special apparatus which you see upon the table, was constructed to 
hold the metal slips when under examination. Its peculiarity con¬ 
sisted in an automatic combination of accurately proportioned screws 
acting in opposite directions, by means of which a single motion of 
the hand sufficed to cause the upper and lower electrodes to approach 
or recede from the central line of contact in an equal degree. Its 
object was to admit of the electrodes being separated to any desired 
extent, while preserving the line of vision through the spectroscope 
directed to the centre of the spark. I found that while a decided 
difference in the spectral lines could be observed between alloys of 
comparatively wide variation, I was unable to detect any appreciable 
distinction between those varying but slightly in their composition. 
Several curious and unexpected anomalies were noticed in the course 
of this investigation, but the principal source of difficulty appeared 
to be owing to the infinitesimal amount of metal vaporized by the 
spark. I found, for instance, that when small electrodes were accur¬ 
ately weighed upon the delicate assay balance a thousand sparks might 
be passed between these points, each spark producing a brilliant 
spectrum of the metal, and yet the total loss in weight was only one- 
thousandth part of a grain; that is to say, each spark vaporized one- 
millionth part of a grain ! Now, as I have already shown you, it is 
necessary to determine assays of the precious metals to the one-ten 
thousandth part of the normal assay weight, and it is hardly con¬ 
ceivable that a discrimination to the one-ten thousandth part of the 
spark assay weight or the one-ten billionth of a grain is practically 
possible. Even if it were so, the present state of metallurgy is not 
sufficiently perfected to enable us to mix the alloy so homogeneously 


351 


Crova—Calorific Intensity of Solar Rays. 

that we could safely assume that a test on such an atomic scale would 
correctly represent the value of a large deposit. 

While there are several apparent paradoxes which have not as yet 
been explained, judging by former experiences in which even more 
mysterious problems have been resolved by study, we are surely war¬ 
ranted in anticipating, that when a larger number of observations, to 
be made, perhaps, by many experimenters, shall have been collated, 
the true scent may suddenly be struck, which shall discover the 
desideratum of quantitative spectroscopic analysis of metallic alloys.. 


CALORIFIC INTENSITY OF SOLAR RAYS. 


Note of M. A. Crova. 


“ In previous communications, 1 I have indicated the methods of 
observation and of calculation, which I have adopted in my researches. 
It was interesting to inquire what are, at different epochs of the year, 
the quantities of heat received during a day by the horizontal surface 
of the soil; these determinations may excite an interest in the study 
of the phenomena of vegetation, and furnish facts for the study of the 
propagation of solar heat in the earth. With this aim, I have calcu¬ 
lated the observations made during two normal days, during which 
the sun shone without interruption, days remarkable for the continuity 
of the atmospheric diathermaneity, and chosen as near as possible, 
the one to the winter solstice, the other to the summer solstice. 

“I have already given 11 the measurements of calorific intensity in 
the solar rays, made at Montpellier during the 4th of January, 1876. 
This series was remarkable for the clearness of the sky and the gen¬ 
eral symmetry of the hourly curve of calorific intensities. The 
total quantity of heat received during the whole day, normally to the 
direction of the solar rays, upon a surface of 1 sq. centimetre, could 
be obtained by integrating the hourly curve, but it is more simple 
and equally precise to trace the hourly curve of the calories from 
sunrise till sunset, and to weigh the area of the curve thus obtained. 
If the paper is of uniform thickness, the weight of this area, compared 
with the weight of the rectangle in which it is inscribed, will give the 


1 Comptes Rendus, lxxxi, p. 1205, and lxxxii, pp. 81 and 375. 

il Memoires de VAcad, des Scietices et Retires de Montpellier , 1876, p. 61. 










352 


Chemistry , Physics , Technology , 

total value of the calories received in this interval, normally to the 
sun’s rays; by previously weighing rectangles of different surfaces, 
from the paper which I used, I assured myself of the proportionality 
of their surfaces to their weights. 

“ On the other hand, I traced upon the same paper the curve which 
gives, for each observation, the product of the calorific intensity of 
solar radiation by the cosine of the sun’s zenith distance at the middle 
of the observation; the weight of this curve measures the total heat 
received by 1 sq. centimetre of the horizontal surface of the soil, from 
the moment of sunrise till that of sunset. 

“ I made a complete series of observations on the 11th of July, 
1876, near the shore of Palavas, 12 kilometres from Montpellier; 
this day was remarkable for the clearness of the sky, and the stead¬ 
iness of alight northwest wind that weakened the disturbing influence 
of the sea breeze, which was not perceptible at the surface of the 
ground. The horizon being free in all directions, I was able to 
measure, without interruption, from sunrise to sunset, by means of two 
actinometers carefully compared and simultaneously observed, the 
calorific intensity of the direct radiation, and that of the part which 
was transmitted through a layer of water 1 centimetre thick. 

“ The observations of July 11th show the want of symmetry peculiar 
to summer days ; after weighing the hourly curves of the morning and 
evening calories, and doing the same for the curves of the products 
of calorific intensities by the cosine of sun’s zenith distance, I cal¬ 
culated the total value of the quantities of heat received during this 
day, normally to the solar rays and by the horizontal surface of the 
soil, upon an area of 1 sq. centimetre. The results of these measure¬ 
ments for the two days are as follows: 

“January 4th, 1876. 

Heat received on 1 sq. centimetre. 

Normally. On the surface of the soil. 

1. From sunrise till noon, 264-4 78 9 

2. From noon till sunset, 270 6 82 3 

3. From sunrise till sunset, 535*0 161*2 

“ The calories received normally varied between 0 and 1*29, in 9 
hours of exposure. 

“ The calories received on the earth’s surface varied between 0 and 
0-53, in 9 hours of exposure. 

“ The heat received on the earth’s surface, is -301 of the normal heat. 






Academy of Natural Sciences. 


353 


“July 11th, 1876. 

Heat received on 1 sq. centimetre. 

> - ' - \ 

Normally. On the surface of the eolL 

1. From sunrise till noon, 451*5 293*5 

2. From noon till sunset, 424*9 280 6 

3. From sunrise till sunset, 876*4 574*1 

“ The calories received normally varied between 0 and 1*21, in 15 
hours of exposure. 

“ The calories received on the earth’s surface varied between 0 and 
1*10, in 15 hours of exposure. 

“ The heat received on the earth’s surface, is *655 of the normal heat. 

“ The heat received normally on Jan. 4th, is *610 of that received 
on July 11th. 

“ The heat received on the earth’s surface on Jan. 4th, is *281 of 
that received on July 11th. 

“ These results give a precise measure of the irregularities pro¬ 
duced, in summer and in winter, by the obliquity of the solar rays, 
and by the duration of the sun’s appearance above the horizon, 
between the absolute values of the intensity of solar radiation, and 
between the ratios of the quantity of heat sent directly, to that which 
is received upon the horizontal surface of the soil.”— Comptes Rendus , 
March 12th, 1877. C. 


Academy of Natural Sciences. —Part III of the Proceedings, 
for 1876, contains: Self-fertilization in Mentzelia ornata, Meehan; 
Direct Growth Force in Roots, Id.; Interpretation of varying forms, 
Id.; On the Marine Faunal Regions of the North Pacific; An Intro¬ 
ductory Note to the Report on Alaskan Hydroids, by Mr. Clark, 
Dali; Report on the Hydroids collected on the coast of Alaska and 
the Aleutian Islands, by W. H. Dali, U. S. Coast Survey, and party, 
from 1871 to 1874, inclusive, Olarh; On the Extension of the Seminal 
Products in Limpets, with some remarks on the Phyllogeny of the 
Docoglossa, Dali; Descriptions of some vertebrate remains from the 
Fort Union Beds of Montana, Cope; On Conglomerate No. XII, 
Young; The Australians, Pickering; On Sonomaite, Goldsmith; Ex¬ 
plorations in S. America, Cope; On Boussingaultite and other min¬ 
erals from Sonoma County, Goldsmith ; Report on Insects introduced 








354 Chemistry , Physics , Technology , etc . 

by means of the International Exhibition, announcing u with moderate 
certainty, that no evil results will occur to our agricultural interests, 
from any introduction of foreign insects, by means of the Centennial 
Exhibits,” Le Conte , chairman; Notes on a Cirripede of the Cali¬ 
fornia Miocene, with remarks on Fossil Shells, Conrad; Notes on 
American Cretaceous Fossils, with descriptions of some new species, 
Grabb; On Ozocerite, Leidy; On Hyraceum, Id.; On Itacolumite y 
describing specimens “ reported to be from Mariposa Co., Cal., which 
are interesting and worthy of note by reason of the new locality, and 
as showing the peculiarities of this kind of sandstone in a marked 
degree,” Blake; Mineralogical Notes, Willcox; Impurities in 
Drinking Water, stating that “ during the last eight years, whenever 
the Schuylkill has been covered with ice, he observed that the water 
supplied by the city possessed a disagreeable odor and taste like 
chlorine,” Id.; On Excrescences and Eccentric Wood Growths in the 
Trunks of Trees, showing that “ there was no reason why cells, pre¬ 
destined, under ordinary circumstances, to be merely bark cells, in 
their change from wood cells should not occasionally retain enough 
of growth force to carry on a feeble wood constructing system of 
their own,” Meehan; Pickeringite from Colorado, Goldsmith; Ep- 
somite on Brick Walls, accounting for the whitish incrustation at the 
beginning of winter, Id.; Notes on Fishes from the Isthmus of Pan¬ 
ama, Gill; On some Extinct Reptiles and Batrachia from the 
Judith River and Fox Hills Beds of Montana, Cope; Our Sidereal 
System, and the Direction and Distance to its centre, Ennis. C. 


Prize for a method of Detecting Adulterations of Butter.— 

The bureau of the LeipzigPharmaceutical Union, offers a prize of 300 
marks for the discovery of a sure and practical method for the detection 
of adulteration of butter by other fatty substances. Professors 
Dr. Heintz, in Halle, and Dr. Knop, in Leipzig, have consented to 
act with Herr Kohlmann as judges in awarding the prize. Each 
competing essay is to be provided with a motto and accompanied by 
a sealed note, containing the motto on the outside and the author’s 
name on the inside, and both are to be forwarded to Herr Kohlmann, 

Apothecary, in Leipzig-Reudnitz, before September 30th, 1877._ 

Dingier s Polyt. Jour., 223, 2, Jan., 1877. C. 





























































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THE JO TONAL 

* 4 

f aOK THE 

t J r 

FRANKLIN INSTITUTE. 


Devoted to Science and the Mechanic Arts 

The Journal of the Franklin Institute is issued in monthly numbers, 
of seventy-two pages each, largely illustrated, forming two volumes annually. 

Its object is to encourage original research, and disseminate useful knowledge 
in all matters relating to the practical application of science, but more espe¬ 
cially to engineering and the mechanic arts. 

The number for December, 1876, completed the one hundred and second vol¬ 
ume of the Journal, and closes the fifty-first year of its existence, and its next 
vo'ume will commence under very favorable auspices. 

Under the direction of the Committee on Publication, with its list of able 
scientists and engineers, as contributors, largely increased, and with the fact 
that it is the only Technological Journal published in the United States without 
any private pecuniary interest, sufficient assurance is given that it will main¬ 
tain its high position as a leading organ of technology and a standard work of 
reference. 

Beside a great variety of matter of general interest, the Journal contains the 
proceedings of the meetings, and has contributed in a very large degree to the 
usefulness of the Institute, which should especially commend it to the support 
of the members. 

The Committee on Publication are desirous of increasing its circulation, 
being fully assured that it will more than repay the small outlay required to 
secure it. 

As the Journal circulates extensively among scientific men, engineers and 
manufacturers advertisers will find it to their advantage to avail themselves of 
its advertising columns. 

SUBSCRIPTION PRICES. 

To Members, S3.00 per Year. Single Copies, 25 cents. 

To Non-Members, 5.00 per Year. Single Copies, 50 cents. 



RATES OF 

ADVERTISING. 



1 Year. 

6 Months. 

3 Months. 

1 Month. 

1 PAGE, 

$00 00 

$32 00 

$18 00 

810 00 


32 00 

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14 00 

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14 “ 

18 00 

14 00 

10 00 

4 00 


Communications for the Journal and busines* letters should be addressed to the 
Secretary of the Franklin Institute, Philadelphia, Pa 


